All are interesting, and possibly solutions to this issue..
I returned to the range for the first time since the issue began.. 7 magazines, in question. i loaded three rounds in each magazine, to keep it short. 2 of the magazines failed to open the slide after last round. I opened the two magazines right there , and looked at the springs to make sure the top was facing up and forward, and the followers in the right direction.. I re-assembled those magazines, and tried again. This time the slide opened after last round..?
I did not have enough time to try and re-create the issue again..
By the way, these two magazines have had the springs replaced by wolf......? But, I replaced the springs in these two magazines, because they did not feed properly....
This M-9, only has a few thousand round in and out. but is 20 years old.. Purchased new..